1. Field of the Invention
The present invention relates to the machines and material handling methods for homogeneous particle mixing of batch quantities. More particularly, the invention relates to vertical fluidized batch mixers and related batch processes of material handling.
2. Description of the Prior Art
In the production of powder coatings, toners, engineered polymers and color concentrates, ingredient size reduction and homogeneous blending are primary objectives. Also important are the prevention of ingredient resegregation, equipment cleanability and product transfer mobility. For high value products that require extreme constituent control, vertical shaft batch mixers are the tool of choice for most practitioners.
Many processes thrive on high intensity mixing which, definitively, requires a mixing blade tip speed of greater than 20 m/sec. The mixer blade tip velocity for medium intensity mixers is usually defined as within the range of 8-10 m/sec. Driving mixing blades through a large quantity of powdered solids at such blade tip velocities requires a significant magnitude of driving power and correspondingly large drive motors that are supported on the same structure as the mixing vessel. The principle behind high intensity mixing is to generate a large amount of energy in the product using an impeller, when, at the same time, the material is suspended and fluidized by the vortex created in the vessel. Sheared mixing and dispersed mixing take place while energy is exchanged between the mixing blades and the material, between the material and the vessel and between the material particles. Steam, oil and hot or cold water may be circulated through a vessel jacket to induce effective heating or cooling of the material during the mixing process.
Traditional designs for successfully serving these functions such as the Model VFM High Intensity Mixer by Reliance Industries of Stafford, Texas have been difficult to discharge the mixed product and extremely difficult to clean. In some cases, color contamination of less than 0.05% due to inadequate cleaning may waste an entire vessel batch. Consequently, each mixing unit may be unavailable for production for hours during a clean-up period although the actual mixing procedure requires only a few minutes.
Prior art machines designed for operating with simple, interchangeable vessels such as Model RC by Reliance Industries mounts the motor and drive assembly on a head plate that must be rotated to invert the vessel and deposit the mixture ingredients around the mixing blades. The entire pivoted mass, therefore includes not only the motor and drive assembly but also the mass of the vessel and material contents. While mixing is taking place, the consequential load and vibration is carried by bearings necessary to facilitate rotation of the assembly. The magnitude of applied power and mixing intensity is therefore limited.